Re: interface Vlan vs L3 port switch

Thanks Andrew,

The topology is something like this:

SW1
SW2

L3port*SW1* L2port*SW1*(Vlan2) <------Dot1q trunk------> L2port*SW2*(Vlan2)
L3port*SW2*
      |
|
| |

|_________|
|_____________|
        Physical
cable1 Physical
cable2

, and obviously the Layer3 ports of the 2 switches are on the same ip
network. As you are directly interconecting 2 ports of each switch,
is there a possible risk of having a loop, maybe at booting, when the
switches are turnning on? And what happens with the STP, may it block some
port or cause the systems to continously complain about vlan mismatch?

I never used a scenario like this, nor in lab environments... to me it seems
a "bad" solution, but it would be helpfull if you can point the
problems this topology could cause, if you clearly see anyone.

Regards

Juan
2011/5/18 ALL From_NJ <all.from.nj_at_gmail.com>

> Do I understand the topology like this:
>
> L3port-SW1 <-> L2-SW2 <-> L3port-SW3
>
> Having any L3 device connect to your L2 switch is fine.
>
> Having two L3 devices connecting to your L2 switch and configuring these
> ports within the same VLAN means that they can talk just fine ;-)
>
> I would suggest to use portfast on the interfaces connecting to the L3
> devices. You may also consider bpdufilter as well as a default for when
> using portfast.
>
> Is it a good design in your network? Humm ... you would know best.
>
> HTH,
>
> Andrew
>
> .
>
> On Wed, May 18, 2011 at 2:42 AM, <fferrer10_at_gmail.com> wrote:
>
>> Hi Guys,
>>
>> I have some doubts about a config a colleague of me is doing using L3
>> Catalyst
>> switches: in order to have IP communication on 2 linked switches, he is
>> using a
>> L3 port on each one, and conecting this port (with a cable) to a L2 port
>> of a
>> common vlan (in each switch)... As the vlan crosses the switches and has
>> L2
>> ports on each one, he can connect another L3 port, with the same ip
>> network, to
>> a port of the second switch and have the 2 switches speaking IP in this
>> vlan
>>
>> My first impression was "this can be or could be a potential loop, why
>> not
>> using the Vlan interface, that is done for this cases?"... Anyway, since
>> he
>> told me that is plannig to run BGP and he does not like a vlan interface
>> as
>> bgp speaker, i am wondering if there are reasons to totally reject this
>> strange/curious design.
>>
>> Anyone can provide help to see the possible problems of this scenario on a
>> production environment, please?
>>
>> TIA and best regards.
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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>
>
> --
> Andrew Lee Lissitz
> all.from.nj_at_gmail.com
>

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